Chat: understand user intent

[marco-m-pix4d]

This fixes the limitation I mentioned this morning in the standup, that @sambarluc and myself discovered in a test pipeline with the previous release candidate.

Before this change, if on a specific put the user wanted to send a notification message, for example:

    - put: cogito
      inputs: [repo.git, app]
      params:
        state: success
        chat_message: "Perftracker registration of X"

He would be forced to actually make the pipeline spammy by adding state success to source.chat_notify_on_states.

To solve this, we had two options:

1. Add put.params.chat_notify_on_states, but this would look ugly:

   - put: cogito
     inputs: [repo.git, app]
     params:
       state: success
       chat_notify_on_states: [success]        <== well it is obvious, no?
       chat_message: "Perftracker registration of X"

2. Understand what the user wants: it is obvious that at least one of chat_message or chat_message_file is set, then the user wants to send the chat message in this specific put. Note the specific == NON in a job on_xxx handler.

In this PR we implement with option 2.